The present invention relates to a tube connecting structure between a resin tube and a tubular mating member. The present invention relates to, in detail, a connecting structure between a resin tube, such as an automotive tube such as, for example, a fuel tube, and a tubular mating member such as a metal pipe.
A rubber tube has been conventionally used as an automotive fuel tube or the like. In recent years, however, the rubber tube tends to be replaced by a resin tube made of hard resin, such as nylon, having good gasoline permeability resistance or the like due to its lower cost. The same thing occurs to other automotive dedicated tubes such as an air tube.
Conventionally, as disclosed in, for example, U.S. Pat. No. 5,161,833 and U.S. Pat. No. 4,991,882, in case of fluid-tight connecting a resin tube of this type to a mating member, the following connecting structure is known. A containing portion is formed such that a retaining member is retained on axial one end of an axis bore of the cylindrical housing and a ring-shaped elastic seal member, such as an O ring, is retained axially inward of this retaining member. When the insertion end portion of a tubular mating member is inserted into the interior of the retaining member from one end of the housing thereof, the retaining member is snap-engaged with an annular stopper on the insertion end portion to thereby fluid-tight connect the mating member to the one end portion of the housing. At the same time, an engaged one end portion having an outer peripheral surface smaller in diameter than the one end portion is formed integrally with the other end of the housing. The inner peripheral surface of the one end portion of the resin tube is press-fitted into the engaged end portion and the resin tube is fluid-tight connected to the other end portion of the housing. The housing having the retaining member retained on one end portion and the tubular mating member inserted into the one end portion of the housing form a quick connector as a whole. Normally, a tube connecting structure using the quick connector is widely used.
The above-stated quick connector is complex in structure and expensive. Due to this, there has been proposed a method of directly connecting a resin tube to a tubular mating member not using the quick connector but using a simple member. This is disclosed in, for example, the published specification of EP0840051. Specifically, it discloses a hose connecting structure in which the first engagement portion of a tubular mating member is formed integrally with the end portion, which is blow-molded, of a resin tube, an elastic seal member such as an O ring is installed into an annular groove, which is also blow-molded, and the second engagement portion of the tubular mating member is engaged with the first engagement portion of the resin tube, thereby connecting the resin tube with the tubular mating member.
In the tube connecting structure connecting a resin tube with a tubular mating member using the conventional quick connector, the engaged end portion of a cylindrical housing is press-fitted into the inner peripheral surface of one end of the resin tube. The problem with this structure is that the connecting portion is lacking in the reliability in terms of pulling resistance and sealing property. And the tube connecting structure using the conventional quick connector is complicated in structure and requires a number of parts. As a result, the structure becomes expensive. It also requires two liquid-tight seal connecting portions axially separated from each other, with the result that the tube connecting structure becomes longer in axial direction. In these circumstances, demand for a tube connecting structure which is more compact, requires lower cost and ensures that a resin tube is liquid-tight connected to a tubular mating member is rising.
By the way, the tube connecting structure proposed in the published specification of EP0840051 as stated above does not employ a conventional quick connector mentioned above. Thus, it is relatively simple in structure and has an excellent is sealing property. This is because the resin tube is directly connected to the tubular mating member by putting an elastic seal member between the resin tube and the tubular mating member.
However, due to the fact that the first engagement portion is formed integrally with the end portion of the resin tube so as to engage the resin tube with the tubular mating member, the structure of EP0840051 requires bothersome blow molding. That is, it requires setting a resin tube into a blow molding die and then blow molding or injection molding the first engagement portion, or setting the first engagement portion, which has been molded independently in advance, into a blow molding die and then extruding parison into the blow molding die to thereby blow-molding the first engagement portion. Thus, the structure is disadvantageous in that it has poor productivity and that the merit of low cost is thereby lost.